If you are used to working in languages like Jave or libraries like OpenSSL, then you might want to visit the Init-Update-Final wiki page. Crypto++ provides the transformation model, but its not obvious because its often shrouded behind Pipelines.

Note: if your project is using encryption alone to secure your data, encryption alone is usually not enough. Please take a moment to read Authenticated Encryption and understand why you should consider using a block cipher and mode like CCM, GCM, or EAX.

Pipelines

You can also use stream ciphers in a Pipeline. Below is an example of Panama participating in a pipeline. Internally, StreamTransformationFilter calls ProcessData on the incoming data stream. The filter also buffers output if there is no attached transformation or sink.